Modulation system



Feb. 18, 1941.

G. L. DAVIES MODULATION sYs'rau Filed July 18, 1938 gnaw/mm Gollzer L. D i ?93343 I Patented Feb. 18, 1941 PATENT OFFICE MODULATION SYSTEM Gomer L. Davies, Cleveland, Ohio, assignor to Washington Institute of Technology,

Inc.,

Washington, D. 0., a corporation of Delaware Application July 18, 1938, Serial No. 219,861

' 8 Claims.

This invention relates, generally, to the modulation of radio frequency currents and, more particularly, is intended. to provide a method of and means for modulating currents transmitted at ultra-high frequencies.

It is the particular object of this invention to provide a method and means for modulating radio frequency currents with carrier suppression, in which method the radio frequency current will be modulated by periodically applying a short circuit to the connection between the radio frequency source and the load to thereby effect intermittent power transfer from the source to the load, or by intermittently de-tuning the circuit connecting the source and the load from the operating frequency. Methods of and means for efiecting modulation in this manner are described and claimed in the co-pending application filed by Frank G. Kear and myself, Serial No. 177,782.

Other objects and features of noveltyof the invention will be apparent from the following description and the annexed drawing, it being clearly understood, however, that the invention is not limited in any way by such description and drawing, or in any other way than by the appended claims.

Referring to the accompanying drawing, in which similar reference numerals refer to like parts, i

Fig. 1 is a circuit diagram illustrating the application of my invention to a single line circuit,

Fig. 2 is a circuit diagram illustrating an unbalanced input and balanced outputcircuit, which is generally similar to the circuit disclosed in Fig. 1;

Fig. 3 is a circuit diagram illustrating my invention as applied to a balanced line circuit, and

Figs. 4 and 5 are views illustrating forms of modulators which may be employed in carrying out my invention.

It has heretofore been proposed, and is now well known, to effect the modulation of radio frequency currents by mechanical or electrical means which act to connect and disconnect the source of current from the load circuit at the modulation frequency. One method and means for modulating radio frequency current according to the aforesaid general method is disclosed in the co-pending application referred to hereinbefore, and such method and means comprises, broadly, the periodic application to the connection between the source and the load of a shortcircuiting network, thereby intermittently. preventing the passage of current to the load.

The present invention employs the modulating means disclosed in the aforesaid co-pending application for effecting the modulation of high frequency currents with carrier suppression. A single line circuit for carrying out the invention is disclosed. in Fig. 1 of. thedrawing and it will be seen that the circuit there disclosed comprises a source of radio frequency current I and a load circuit 2, these being connected by transmission lines 3, 4 which are connected between the output terminals of the source and the input terminal of the load circuit. The modulation of the radio frequency current output of the source I is efiected by alternately short-circuiting each of the transmission lines 3, 4 at any points B, B along the length thereof, which points are preferably spaced from the input ends of the lines by any distance which is a multiple of a quarter wave lengthof the current output of the source. The

shortcircuiting of the line is effected by con-'* necting to the transmission lines, at the points B, B variable capacity coupling devices comprising fixed capacitatively related plates 6, 6, which are connected respectively to the conductor and grounded shield of transmission line 3, fixed capacitatively related plates 1, I which are connected respectively to the conductor and grounded shield of transmission line 4, and rotor 5. The lines connecting the pairs of plates and the transmission lines are of known electrical length and, in order to avoid the necessity of exactly dimensioning these lines and the lines between the output of the source and the points B, B, additional loading circuits 8, 9 are connected to the transmission lines 3, 4, respectively, at the points B, B. As disclosed "in the aforesaid copending applicatiomthese loading circuits preferably take theform of short-circuited lines, the terminals of which are connected to the conductor and shield portions of each of the transmission lines 3, 4 respectively. The lengths of the lines 8, 9 are so adjusted, as fully set forth in the aforesaid co-pending application, that the total combined length of each of lines 8 and 9 and the length of the line connecting the associated capacity device thereto will be such that the impedance across each transmission line at point B varies from zero to infinity.

The plates 6, 6 are capacitatively related, as are the plates 7, I, and the plates of the rotor 5 are so positioned that they may pass between the .platesof each pair as the rotor revolves, as illustrated in Figs. 4 and 5. The two pairs of plates are so arranged with respect to each other that when the one plate of the rotor 5 is disposed between the plates of one pair,,the second rotor plate is entirely removed from the plates of the second pair, all as illustrated in Figs. 1, 4 and 5. In the operation of the system disclosed in Fig. 1 the operation of the rotor 5 will cause the capa-citative coupling between plates 6, 6 to vary from a maximum to a minimum value as one or the other of the rotor plates moves from a position completely covering these plates, as illustrated, to a position completely, removed therefrom. In the same manner, the operation of the rotor causes the capacitance between plates 1, to vary from a, maximum to a minimum value.

If it is assumed that, at any instant, the terminal b of source is positive and that the rotor 5 is in the position illustrated, in which the capacitance between plates 1, is a minimum, current at the frequency of the source will flow through transmission line 4 and load 2 to ground, flowing through the load in the direction of the arrow X1. As the movement of the rotor continues, causing the plates thereof .to decreasingly cover the stator plates 6, 6 and increasingly cover the plates 1, 1, the capacitance between plates 8, 6 will decrease while that between plates 1, 1 will increase, thereby causing a decreasing amount of current to be passed by transmission line 4 and an increasing amount to be passed by line 3. The phase of the current in load circuit 2 will not change so long as line 4 passes more current than line 3, and the envelope of the resultant current in the load circuit will be a sine curve. When the rotor has moved .to a position in which one of the plates thereof equally covers the plates of pair 3, 6 and those of pair 1, 1, the currents passed by lines 3 and 4 will be equal and the resultant current in the load circuit will drop to zero. When the rotor has moved to a position at right angles to that illustrated in Fig. 1, in which position the capacitance between plates 6, 3 will be a minimum and that between plates 1, 1 will be a maximum, and if it is assumed that at that instant the terminal b of the source is again positive, current will flow from ground at IU through the load circuit in the direction of arrow X2 and through transmission line 3 to the negative terminal a of the source. The phase of the current has now been reversed and will not again change until after the operation of the rotor causes equal currents to be passed through transmission lines 3 and 4.

It will be apparent that the envelopes of the currents flowing in the transmission lines 3, 4, and consequently the currents fiowing in the load circuits in the directions of the arrows X1 and X2, will increase and decrease in opposition and, under proper conditions, each of such envelopes will be a sine curve. As described, the phase of the resultant current in the load circuit will be reversed as the resultant current passes through zero, and it will therefore be seen that the circuits and mode of operation disclosed will provide modulation with carrier suppression.

A balanced output circuit may be employed in place of the unbalanced output circuit illustrated in Fig. 1 if an unbalanced input circuit is employed, and such a circuit is disclosed in Fig. 2, in which figure the parts are referred to by the same reference numerals as are used in Fig. 1.

In Fig. 3 of the drawing there is disclosed a balanced line circuit for modulating radio frequency current with carrier suppression and supplying the side band frequencies to a load circuit, such as an antenna system. A source of radio frequency current is'shown at 20 and a load circuit at 2|. Each out of the output terminals of the source are connected to each of the terminals of the load circuit, terminal a of the source being connected to terminals 0 and d of the load through shielded transmission lines 22 and 23, respectively, while terminal b of the source is connected to terminals 0 and d of the load through shielded transmission lines 24 and 25, respectively.

Means are provided by the invention for modulating the radio-frequency current supplied by the source to the load 2|, and such means comprise a variable capacity device denoted generally by reference letter A and comprising a rotor 26 and two pairs 21 and 28 of fixed plates which are arranged within the path of the rotor and which are so disposed that when one plate of the rotor is fully disposed between the plates of one pair, the second rotor plate will be entirely removed from the plates of the second pair of stator plates. The plates 21, 21 are connected, respectively, to the two transmission lines 23, 24 at points B, B which are preferably spaced from the source 20 by an odd number of quarter wave-lengths of the output wave of the source, such connections being made by transmission lines 29, 30. The plates 28, 28 are connected to the transmission lines 22, 25, respectively, at points C, C which are preferably spaced from the source 20 by an odd number of quarter wavelengths of the output wave of the source, such connection being made by transmission lines 3|, 32. In accordance with the principles set forth in the aforesaid co-pending application, a loading circuit 33 is connected between the transmission lines 23, 24, at the points B, B, and such circuit is so adjusted that the electrical length thereof plus the electrical length of the lines 29 and 30 will be such that the impedance of the transmission lines 23, 24 at points B, B will vary from zero to infinity. A similar loading circuit 34 is connected across transmission lines 22 and 25 at points C, C and this circuit is so adjusted that the total electrical length of the circuit 34 and the lines 3|, 32 will cause the impedance of the transmission lines 22, 25 at point C, C, to vary from zero to infinity. The loading circuits 33, 34 are inductive in nature and may be formed or short-circuited transmission line, as disclosed.

In the operation of the balanced line system disclosed in Fig. 3, it may be assumed that at any instant the terminals a and b of the source are positive and negative, respectively, and that the rotor 26 is in a position illustrated, in which the capacitance between plates 28, 28 is a minimum, thereby having no efiect whatsoever on the passage of current through transmission lines 22 and 25, while the capacitance between plates 21, 21 is a maximum thereby causing the total impedance at point B to be a minimum and hence short-circuiting the transmission lines 23, 24 at point B, B and preventing the transmission of current therethrough. Under these conditions, current will flow from terminal a through transmission lines 22, load 2| and line 25 to terminal b, flowing through the load 2| in the direction of the arrow X3. No current will be transmitted through lines 23 and 24 and, at this time, no current will flow in the load circuit in the direction opposite to that of the arrow X3. As the movement of the rotor continues the capacitance conditions between the plates 28, 28 and 21, 21 will progressively change until, when the rotor is in such a position that one of the plates thereof completely covers the plates 28, 28, current will flow from output terminal a through transmission line 23, load 2| and transmission line 24 to output terminal b, the fiow of current through load 2| being in the direction of arrow X4. It will be apparent that the resultant current in the load circuit at any instant will be in the direction of either arrow X3 or X4 and that the current flow in either direction will vary from zero to maximum, while the current fiow plates to pass therebetween.

in the opposite direction will vary from a maximum to zero. If proper conditions obtain, the envelopes of the two currents flowing in the load circuit will be sine curves. Regardless of whether this condition obtains, the resultant current in the load circuit will reverse in phase as the resultant current passes through zero.

In Figs. 4 and 5 of the drawing are illustrated embodiments of variable capacity devices which may be employed in efiecting modulation according to the present invention. In Fig. 4 is disclosed such a device comprising two pairs 40, 4| of stator plates and a rotor 42 having plates 43, 44 at the opposite extremities thereof. The platesof each pair are superposed and are spaced apart sufficiently to permit the rotor plates 43, 44 to pass therebetween. In the construction disclosed in Fig. 4 the plates are shaped as arcuate segments and the axis of one pair of plates is at right angles to the axis of the second pair. i

In Fig. 5 there is disclosed a second form which the variable capacity device may take. In this embodiment there are two pairs 50, 5| of stator plates, the plates of each pair being superposed and being spaced sufficiently to permit the rotor The stator plates are shaped as arcuate segments and theaxis of one pair is disposed at an angle of 135 to the axis of the second pair. The rotor portion of this device is provided with. four radial arms each of which is spaced from adjacent arms and each of which is -provided,'at its outer extremity, with a circular plate, all of such plates being denoted by numeral 52 in the drawing. The variable capacity device illustrated in Fig. 5 will provide'the same functions and effects as that illustrated in Fig. 4 if the rotor thereof is operated at one-half the speed at which the rotor of the device of Fig. 4 must be operated. The pairs of plates 48, 40 of Fig. 4 and 50, 5| of Fig. 5 correspond to the pairs of plates illustrated diagrammatically at 6, 6 and I, 1 in Fig. 1 and at 2121 and 28, 28 in Fig. 3.

While I have illustrated and described a number of embodiments which my invention may take, it will be apparent to those skilled in the art that other embodiments, improvements and modifications may be made and practiced therein, without departing in any way from the spirit or scope of the invention, for the limits of which reference must be had to the appended claims.

What I claim is:

1. A system for" supplying modulated radio frequency energy with carrier suppression to a load circuit, comprising two shielded transmission lines connecting the terminals of a source of radio frequency energy to the terminals of the load circuit, variable capacity devices each connected across the conductor and shield of one of said lines, and means for inversely varying the capacities of said devices at a pre-determined rate to thereby cause the currents passed through said lines to be varied inversely at the pre-determined rate.

2. A} system for supplying modulated radio frequency energy with carrier suppression to a load circuit, comprising two shielded transmission lines connecting the terminals of a source of radio frequency energy to the terminals of the load circuit, a variable capacity device and an inductive circuit connected between the con- 'ductor and shield of each of said lines, and means for inversely varying the capacities of said devices at a pre-determined rate to thereby cause the currents passed through said lines to be varied inversely at the pre-determined rate.

3. A system for supplying modulated radio frequency energy with carrier suppression from a source of radio frequency energy to a load circult, comprising two pairs of variable impedance transmission lines connecting the terminals of the source to the terminals of the load circuit, two capacity devices each of which comprises two fixed plates which are connected across a different pair of said transmission lines, a rotary device associated with the plates of both said capacity devices and being operable to vary the capacitance between the plates of each of said .,devices, said capacity devices being so arranged with respect to each other that operation of the rotary device causes the capacitance of said devices to be substantially inversely varied, to

thereby continuously and inversely vary the current passed through each such pair of transmission lines.

4. A system according to claim 3 in which an inductive circuit is connected across each pair of transmission lines at the points of connection thereto of the fixed plates of each capacity dey vice.

5. A system for supplying modulated radio frequency energy from a source of radio frequency energy to a load circuit, comprising two transmission lines connecting the source and the load circuit and each having grounded shielding means, variable capacity means connected between each line and the shielding therefor, and means for continuously and inversely varying the capacities of said means to thereby continuously and inversely vary the currents passed through said lines.

6. A system for supplying modulated radio frequency energy with carrier suppression from a source of energy to a load circuit, comprising at least two two-element transmission lines connecting the source and the load circuit, yariable impedance means connected across each of said transmission lines, and means for continuously and inversely varying said impedance means at a pre-determined rate to thereby continuously and inversely vary the energy passed through said transmission lines.

7. Asystem for supplying modulated radio frequency energy with carrier suppression from a source of radio frequency energy to a load circuit, comprising two pairs of variable impedance transmission lines connecting the terminals of the source to the terminals of the load circuit, two capacity devices each of which is connected across a different pair of trassmission lines, means for continuously and substantially inversely varying the capacitance of said devices, to thereby continuously and substantially inversely vary the energy passed through each such pair of transmission lines.

8. A modulating system according to claim 6, in which each of the variable impedance means is connected across the associated transmission line at a point which is spaced from the source by a distance which is any quarter wavelength of the energy supplied by the source.

GOMERI L. DAVIES. 

